To make the slaw, add the red cabbage, green cabbage, green onion, and cilantro to a large bowl.
In a separate bowl, whisk together the lime juice, olive oil, and a pinch of salt and pepper.
Pour the dressing over the cabbage mixture and toss to combine. Set this aside while you work on the fish. Be sure to give it a stir every few minutes.
To make the fish, pat it dry with paper towels, and place it on a large sheet of waxed paper.
Mix all of the seasonings for the fish in a small bowl, and sprinkle them liberally on top of the fish, gently rubbing it in as you go. Turn the fish over and repeat.
Place a large, non-stick skillet on the stove over medium-high heat.
When the pan is hot, add the olive oil and the butter.
Carefully lay the fish in the pan, and allow it to cook for about 40 seconds.
Continue to cook the fish until it has a dark (but not black) crust of color on the bottom. Gently rotate it around as it cooks to help it evenly brown. This process should take 2-3 minutes.
Gently turn the fish over and place the pan in the oven for 10 to 15 minutes or until the fish is cooked through and easily flakes apart. To be on the safe side, you can insert a meat thermometer into the thickest part of the fish, and it should register 130 - 135°.
To assemble the tacos, place a little slaw in the bottom of the tortilla followed by a few pieces of the fish. Drizzle with cilantro sauce and sprinkle with additional cilantro.
Serve with extra cilantro lime sauce, salsa, sour cream, lime wedges, and cilantro! Whatever you like!